Here's a video discussing molecular polarity and electronegativity at the beginning (11min): CrashCourse Chemistry: Polar and Non-Polar Molecules, on YouTube
Dipole moments tell us, on average, where the electrons in a molecule are. They can also tell us the shape of molecules. For instance, if H2O were linear, the 2 O-H bond dipoles would cancel each other out, and the whole molecule would be non-polar. Since we know water is polar, it has to have a bent shape.
Also, molecular dipole moments are very important for many properties, such as ability to dissolve solutes, melting and boiling points, and reactivity in general. Dipole moments (actually, change in dipole moments due to molecular vibration) are also involved in whether molecules absorb certain energies of light, which is important for the greenhouse effect. CO2 and methane cause climate change because they can absorb IR light. Although these molecules are too symmetrical to have permanent dipole moments, vibrations can produce small temporary dipole moments that allow them to absorb light.
We can measure molecular dipole moments by measuring the dielectric constant of a material (how much the material weakens the Coulomb forces when it is between the charges). Generally, materials with large dipoles have high dielectric constants. In Coulomb's law, the dielectric constant D reduces the force between charges.
F = | kQq |
Dr2 |